Insulated potential coils



Nov. 10, 1959 R. A. ROAD INSULATED POTENTIAL COILS Filed May 18, 1953 an 3 Q ,3 xv N- m INVENTOR.

nited States Patent 2,912,621 lNSULATED POTENTIAL cons Richard A. Road, West Lafayette, Ind., assignor, by mesne assignments, to Duncan Electric Company, Inc., Lafayette, Ind., a corporation of Indiana Application May 18, 1953, Serial No. 355,578

3 Claims. (Cl. 317*158) In some forms of electromagnetic structures, the provision of adequate insulation between the coil and the core around which it is wound presents a problem of both importance and difficulty. For example, in watthour meters, a laminated core structure has a longitudinal portion extending through the coil, and transverse portions extending laterally beyond the ends of the coil. For reasons of economy and electrical efliciency, it is desirable to have the coil fit the core portion within it as closely as is practicable, and extend close to the transverse portions thereof. According to common practice, the coils are wound on paper tubes designed to slide fairly snugly over the core. The tube insulates the coil from the core except at the ends. If there were room to extend the tube sufiiciently beyond the ends of the coil, the insulation at the ends would be adequate, too, but such is not the case. A separate body of insulation can be placed between the ends of the coil and the radially extending core portions, but between this separate body and the tube there would be a short path between the coil and the core along which creepage or arcing could occur. Creepage is the flow of current along the surface of the insulating material, a phenomenon which can occur under some conditions of dampness. For some purposes, it is preferred that the end insulating material be a molded material. It is especailly important to prevent creepage along such materials, because the creepage currents carbonize the material and make it conductive sothat the material itself carries current. This in turn makes more of the material conductive and this cumulative effect can be quickly disastrous.

Although several ways have been developed for overcoming the creepage danger, they are relatively troublesome or expensive, or require special materials which it is not always desirable to use. According to the present invention, the minimum creepage distance is increased to a satisfactory length at little or no extra cost. When the larninations are stamped, the core portion is made slightly narrower by shallow. recesses in the vicinity of the places over which the coil ends will lie. When the core is assembled and the coil applied thereto, the molded insulation, applied as it would have been applied anyway, flows into the shallow depressions provided by the notches in the larninations and thus overlaps the ends of the tube enough to provide the required minimum creepage distance. Along the fiat faces of the larninations, the insulation also flows a short distance under the tube, the space in this instance being provided by insertion of a spacer shorter than the tube. Thus there is provided a satisfactorily dependable insulation, even though the coil is Fig. l is a perspective view of the potential coil portion of a driving element of a watthour meter, partly 2 broken away to show features of this invention in cross section.

Fig. 2 is a face view of one of the laminations of Fig. 1.

Fig. 3 is a fragmentary view of the structure of Fig. 1, showing a section through the coil and insulation parallel to the face of a lamination.

Fig. 4 is a fragmentary view of the structure of Fig. 1, showing a cross section through the coil and insulation along a plane perpendicular to the faces of the lamina tions.

Although the law requires a full and exact description of at least one form of the invention, such as that which follows, it is, of course, one purpose of a patent to cover each new inventive concept therein no matter how it may later be disguised by variations in form or additions of further improvements; and the appended claims are intended to accomplish this purpose by particularly pointing out the parts, improvements, or combinations in which the inventive concepts are found.

General description So that a given number of turns of wire of a given size can be carried around the central core 14 with a minimum average length of turn in the coil 13, it is desirable for the axial length of the coil to be almost as great as the spacing between the transverse portions 16 and '17. The minimum average length of the turns provides a coil of the minimum electrical resistance and therefore greater electrical efficiency, and also reduces the cost of the coil because less copper is used. Furthermore, 'in some instances it might be necessary to extend the coil v13 quite close to the transverse portions 16 and 17 because there would not otherwise be room within the total space provided for the required number of turns and the necessary surrounding insulation.

The present invention is concerned with providing adequate insulation between the larninations and the coil which lies close to the laminations. Coil 13 is conventionally wound on a tube 18 of insulating material such as a suitable paper. The problem of insulation is especially severe when the portions of the coil adjacent the ends of the tube 18 are closer to the laminations than the acceptable minimum creepage distance. Under these circumstances, it becomes necessary to so dispose the in- Insulation flowed along faces Along the faces of the stacked larninations, it is practical to provide space for the insulation to flow along the faces by inserting a wedge 22, preferably formed of insulating material such as vulcanized fiber between the tube 18 and the larninations 12. Such a wedge is desirable in any event so that the coil will be more firmly mounted on the core. It should be understood that according to ordinary manufacturing practice, the coil is wound on a tube preliminarily, and then applied to the core (the larninations being flexed and slipped into place) so that the coil is initially slightly loose on the core. Insertion of the wedge 22 takes up this looseness.

For the purposes of the present invention, the wedge 3 22 is shorter than the tube 18 and is forced into an axially central position with respect to the tube 18 so that room is left for insulation to flow in at 21. The leading edge of the wedge is tapered to facilitate insertion, a 45 beveling from one face to 'the other having been found satisfactory.

Flowing insulation along edges of laminations Although theoretically a spacer similar to the wedge 22could be provided along the edges of the laminations, this would necessitate that the turns of wire be lengthened. It would also reduce the total amount of space provided for the coil by the apertures through the laminations Where maximum dimensions place alimiting factor upon the space which can be provided.

However, in the case of the edges of the laminations, space for the flowed insulation portions 21 can be provided in an even more simple manner. Itis merely necessary to provide notches 23, approximately as seen best in Fig. 2, while stamping out the IaminatiOns -Once the stamping dies are produced for this shape, theprovision of these notches represents no extra cost. 'Now when the wedges draw the tube 18 snugly around the core 14, the notches 23 will leave a space under the ends of the'tubes 18 into which the insulating material may flow.

From the foregoing, it is seen that without any extra cost insulating portions 21' are provided extending all around the central core 14, between it and the tube 18' Thus there is formed, in effect, an insulating sleeve 'integral with the main body of insulation 19, and extendingiin under the ends of the tube 18 far enough so that the minimum surface distance along it betweencoil 13 and laminations 12 is at least asgreat as and preferably considerably greater than the minimum acceptable 'c'reepage distance. i

As a matter of fact if, as is commonly the case, the tube '18 is slightly longer axially than the coil '13, the minimum creepage distance will be increased by the amount that the tube '13 projects beyond the coil 13.'

i To be sure that there is no interruption in the sleeve 21anywhere around the periphery of the central core portion ld, the width of the wedge 22 is preferably at least equal to the spacing'between notches 23, measured trans versely of the core portio'n' 14. In practice, the wedges would usually be made very close to the full Width of themain core portion '14.

I claim:

1. An electromagnetic structure including a core of magnetic and conductive material, a coil surrounding'said core, a tube between the coil and the coreformed of an insulating material, and of approximately the same length along'the core as is the coil, and molded insulation along the ends of the coil and tube and overlapping-the ends of the tube lengthwise of the'core to lengthen the' 4 to receive the overlapping portion of the molded insulation and that points between the notches, lengthwise of the core, extending approximately as close to the coil as the thickness of the tube.

2. An electromagnetic structure including a core formed of a stack of laminations of magnetic and conductive material, a coil surrounding said core, a tube between the coil and, the core formed of an insulating material, molded insulation along the ends of the coil and tube and overlapping the ends of the tube between the tube and the core lengthwise of the core to lengthen the path of current flow along the surface of the molded insulation fromthe coil to the, core, the laminations of said core being notched at" their edges to receive the overlapping portion ofthe molded insulation and extending closer to the coil at points between the notches than at the bottoms of the notches, and spacing members shorter than the tube and positioned intermediate its ends and between it and the stack of laminationsalong the faces core within the tube. V

3. An electromagnetic structure including a core of magnetic and conductive material, afcoil surrounding said 7 core, a tube betweenthe co'il'and the core formed of an insulating material, and insulation along the ends of the coil and tube and overlapping the ends of the tube lengthwise of the core to lengthen the path of current flow along the face 'of the insulation from the coil to the core, said core being notched to receive the overlapping 1,301,135 Karasick Apr. 22, 1919: 1,763,115 Werrnine June 10, 1930 1,978,568 Crossley et al. Oct. 30, 1934 2,138,606 Lanphier Nov. 29, 1938 2,434,511 Osterman et al I an. '13, 1948 2,442,587 Coggeshall et al; June 1, 1948 2,455,355 Combs Dec-7, 1948 2,640,102 Woods et al May 26, 1953 FOREIGN PATENTS 72,798

portion"oflthe insulation and attpoints between the:

notches, lengthwise'of the core, extendingapproximately as, close to the coil as the thickness of the tube; said insulation at each end of the coil extending integrally along" the coil face and between'the tube and the core entirely around the core and having a natural: shape for exact intimate surface contact with both the core and the tube.

References Cited in the file ofthis patent UNITED STATES PATENTS Norway Nov. 11 1947 I UNlTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION November l0, l959 or appears in the that the said Letters It is hereby certified that err ng correction and of the above numbered patent requiri Patent should read as corrected below.

Column 4, line 2, for "that" read at ----a 31st day of May 19600 Signed and sealed this (SEAL) Attest:

KARL H, All-ENE ROBERT C. WATSON Commissioner of Patents Attesting Officer I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION November 1Q, 1959 appears in the that the said Letters It is herebf certified that error correction and of the above numbered patent requiring Patent should read as corrected below.

6011mm 4, line 2, for that read at and sea ed this 31st day of Ma (SEAL) Attest:

KARL Hu ROBERT C. WATSON Commissioner of Patents Attesting Officer 

